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Mirth connect javascript reader

I am using mirth connect 3.0.3 on windows.my requirement is I have a text file in D drive with some name and id as the text I need to pick that file using mirth javascript reader and insert into the database can u please help me to pick the file using javascript reader.
I tried it by using java code and converting that into to .jar file and placed it in the custom-lib folder in mirth connect and importing that in a script but I want to do it without .jar file
I am getting stuck in importing the packages can you help me to pick the file using javascript reader.

You can take two aproaches:
Use a File Reader source insted of JavaScript Reader source, then modify the transformer adding a new step in which insert your file's content into your database.
Use the FileUtil.read method to read file content inside your Javascript Reader source:
var fileData = FileUtil.read('D:\my_awesome_folder\data.txt');
//Do something with fileData

How can I download CSV data from variable to a csv file?

I am using papa parse library. It helped me in converting JSON to CSV but how can I download the same data into a excel file. My data is huge

If I'm understanding your question correctly, you have a CSV file which you now want to tell the browser to download?
Have you looked at https://github.com/eligrey/FileSaver.js/ ?
Allows you to tell the browser to download a wide variety of files.
An example in using it:
var blob = new Blob(myBigCSVFile, {type: "text/csv;charset=utf-8"});
saveAs(blob, "file.csv");
The browser, upon reaching the saveAs function will download the file you specified.

Checkout SheetJS/js-xlsx library.
Supported read formats:
Excel 2007+ XML Formats (XLSX/XLSM),
Excel 2007+ Binary Format (XLSB),
Excel 2003-2004 XML Format (XML "SpreadsheetML"),
Excel 97-2004 (XLS BIFF8),
Excel 5.0/95 (XLS BIFF5),
OpenDocument Spreadsheet (ODS)
Supported write formats:
XLSX, CSV (and general DSV), JSON and JS objects (various styles)

Trying To Read from Excel File in Javascript

In my .js, I want to be able to provide some function with the path, and then be able to read from the .xlsx file. I have tried the FileReader(), but there is no way to specify a local path to read from. Does anyone know of any way to do this? Thanks.

The MDN page for FileReader links to Using files from web applications which has examples.
You specify the local path using a file input:
<input type="file" id="input">
and then
var selected_file = document.getElementById('input').files[0];
var reader = new FileReader();
reader.readAsBinaryString(selected_file);
Obviously a web page cannot specify an arbitrary file on the user's system to read. That would be a massive security risk.

Upload file inside chrome extension

I need to add a browse button inside my Chrome extension. Users click it and choose a file. I then want to retrieve the file contents (bytes) and do some work on it.
I don't want to have to submit the file to a remote server and then get the response (if that's even doable from inside a Chrome extension), it should be all client-side.
Is this doable inside Chrome extensions?

You should be looking at the FileReader API.
The FileReader object lets web applications asynchronously read the contents of files (or raw data buffers) stored on the user's computer, using File or Blob objects to specify the file or data to read.
A very good basic example of using this interface is in this question.
A minimal example: suppose that you have an <input type="file" id="file"> with a text file selected.
var file = document.getElementById("file").files[0];
var reader = new FileReader();
reader.onload = function(e){
console.log(e.target.result);
}
reader.readAsText(file);
If you need methods other than reading as text (i.e. binary data), see the docs.
Also, this is a good overview: Using files from web applications

Regarding your question it is totally feasible to load and process a file within an extension. I implemented it using message passing https://developer.chrome.com/docs/extensions/mv3/messaging/.
Here is an example of how you can implement it, in my case I used the input file to load an excel. This is my public repo.
https://github.com/juanmachuca95/gomeetplus

How to parse JSON file using Javascript

I want to read a JSON file that in my local machinge using Javescript, and parse it to a Javascript object such as this code:
var parsed = JSON.parse(JSON_file);
Is it possible to read the file from the disk? Or there is other methods to do that.
Thanks.

Here is a nice tutorial on how you can do it using HTML5's FileReader API, but there is one constraint: you can only interact with a file selected by the user via a file input field.
http://www.html5rocks.com/en/tutorials/file/dndfiles/